A syringe pump is a device which typically uses an electromechanical drive to advance and/or retract the plunger on a syringe mounted to that device. Syringe pumps perform multiple tasks in medical care and in biomedical research. Syringe pumps represent the most precise and reproducible means of delivering small volumes of fluid into the body or body tissues of animals. A catheter is a hollow, flexible tube, typically made from a biocompatible plastic, that can be inserted into a vein or artery in the body. For example in humans, the insertion procedure can take place quickly and with minimal discomfort if the vein is close to the skin and readily accessible. When the vein is close to the skin, a sharp needle is inserted into the vein and the catheter is inserted through the lumen (interior) of the needle until it exits the needle tip and enters the vein. The needle is then withdrawn, leaving the catheter tip positioned within the vein. The catheter is then secured to the skin to keep it in position.
After insertion, a catheter can be attached to a syringe and/or syringe pump, so that fluid can be delivered through it, or blood withdrawn from it. Examples of the types of fluids delivered to the body, for humans or various other animals, include physiological solutions such as saline (0.9% sodium chloride), Ringer's Solution, Ringer's Lactate Solution, or artificial cerebrospinal fluid. Such solutions can be administered alone, as in cases of dehydration or detoxification, or with supplements, including nutrients such as glucose, or therapeutic drugs intended to be delivered by parenteral administration (i.e. by the intravenous route). The administering and withdrawal of fluids from an animal can be controlled by the use of valves, or other like means for stopping or allowing fluid flow through the catheter. An example of a system that utilizes pinch valves, a syringe, a syringe pump and a catheter to withdraw blood and infuse saline is the Culex Automated Blood Sampling System manufactured by Bioanalytical Systems, Inc. of West Lafayette, Ind. US and disclosed in U.S. Pat. No. 6,062,224.
It is not atypical, especially during biomedical research with laboratory animals, to administer more than one type of fluid. The methods for making a change in solution include: (1) removing the syringe from the syringe pump and replacing it with another syringe filled with the new fluid; (2) removing, rinsing and refilling the syringe with the new solution; (3) inserting another catheter into another blood vessel and attaching another syringe pump to that blood vessel; or (4) attaching two syringe drives to some type of mechanism which allows the user to switch to the output between these drives. In example (4), the mechanism is often a two-way or three-way valve that is actuated by hand, by electric motor, or by a mechanical or electromechanical fluid switch device. Such mechanisms require that the fluid from both syringes pass into and through the device itself, exposing the fluid to the device and exposing the device to the fluid. Such exposure means that the device must be: (1) discarded after use; or (2) thoroughly cleaned between uses to avoid contamination leftover from prior experiments. Depending on the type of materials used in the switching device, it may not be possible to easily sterilize it between uses since not all materials are thermally stable, or resistant to the effects of sterilizing gases, radiation, or cold-sterilant fluids. Thus, it is desired to provide a device and method for delivery of solutions to animals that does not use a mechanism that exposes the switching device to the solution. Further, it is desired to provide a device and method for delivery of solutions that does not require manual operation or intervention.
In pharmaceutical research, with laboratory animals, new drugs in solution can be introduced into the body via a catheter into the bloodstream. This approach provides a means of controlling how much of the drug enters the body because the concentration of drug (e.g. milligrams per milliliter) in the solution will be known and the volume of drug delivered (e.g. milliliters) will be known. When a drug is administered by mouth, it is necessary to perform multiple tests to learn how much of that drug eventually enters the blood stream since there are several factors affecting absorption of the drug through the barrier represented by the gastrointestinal tract. When a drug solution is administered via a catheter, it can be described as a bolus dose, which is a relatively small volume of fluid administered over a relatively short period of time. In the rat, an example of a bolus dose would typically be a volume on the order of less than 3.0 milliliters and a time of less than 5 minutes. When a drug is administered as a bolus dose, its residence time in the body is determined by the rate at which the body can either metabolize it (e.g. via the liver) or excrete it (e.g. via the kidney or bile duct).
Another approach commonly followed is to administer a continuous infusion dose. In this scenario, the volume of fluid administered can be considerably larger, but the rate of flow is usually lower (e.g. less than 10 microliters per minute), and the length of the experiment can extend for several hours or days. When a drug is administered as a continuous dose, its residence time in the body reaches a steady state in which the rate of drug input (determined by flow rate of the syringe pump) is offset by the rate of drug metabolism and excretion.
These methods of delivering drugs to animals have several shortcomings. In many instances, a technician is required to manually introduce the drug into a solution for administration to the animal. Manual operation requires that the technician be present at all times that the drug(s) is(are) to be delivered. For a continuous infusion dose, constant attention by the technician is required to make certain that there is sufficient fluid remaining in the syringe or that the syringe is refilled without delay. Such use of human resources is expensive. Further, the accuracy of drug dose delivery is affected by the technician's skill and experience. Thus, accuracy may be compromised. Also, if more than one drug is to be administered, more than one technician may be required. These issues are further complicated by the need to change a solution and the shortcomings thereof as discussed herein. Therefore, it is desired to provide a device and method of drug delivery that does not require manual operation, is capable of delivery of more than one drug, does not contaminate the solution by requiring the solution to come into contact with a switching device that was exposed to another solution during a prior delivery, and permits for control of the amount and rate of flow of introduction of the drug(s) to the animal.
The need to deliver drugs for pharmaceutical testing purposes extends both to laboratory animals (such as mice, rats, guinea pigs, gerbils, monkeys, and pigs), as well, as humans. Thus, it is desirable that the device and method be useable for all “animals”, where the term “animals” encompasses any mammals (including humans), reptiles, amphibians, or any other animal used for laboratory testing.
There also is a need to deliver fluids to animals other than through a catheter placed in a blood vessel. For example, a catheter or tube may be implanted into the stomach or duodenum of the animal. Thus, it is desired to provide a device and method for drug delivery to an animal that works in combination with all types of “catheters.” As used herein, “catheter” refers to any type of tube connection to an animal's blood vessels and/or any type of tube connection that provides fluid (with or without a drug or drugs therein) to or extracts fluid from any part of the body, body tissues, organs, or blood system of the animal.
For purposes of understanding the effect of a drug on a subject, it is desirable to extract blood samples from an animal that has received the drug. Such samples are useful for a myriad of purposes, including, ascertaining the level of drug present in the blood stream of the animal at any time relative to the original introduction of that drug. Of course, it is also possible that extraction of other body fluids may be desired, such as in determining the level of drug in the bile, or the kidney, or the aqueous humor of the eye, or fluids in the lung, for example. In addition, there are other techniques for taking biological samples based on the use of dialysis probes that involve exchange of molecules but not fluids. Therefore, it is desired to provide a method of drug delivery for animals that works in conjunction with other equipment intended to extract fluid or dialyze molecules from the animal.